The woman, who asked not to be identified, said the savings were up to 35 percent compared with her local supermarket.
She ordered 13 items online from Australia, including pasta, nuts, dried fruit, rolled oats, toothbrushes, shampoo and hair dye.
She then looked up the same items on her Countdown shopping online app.
The shopper told The New Zealand Herald she ordered via Amazon in Australia and received her products within five days.
She paid $A93.30 ($NZ99.47) for her order.
"I only bought items that were included in a free shipping promotion, so I wasn't charged for shipping. According to the receipt, shipping would have added $15," she explained.
The same shopping cart in her local store would have cost her an extra $40, to a total of NZ$139.96.
The best deal was on toothpaste, for which she paid $A2.50 ($NZ2.69).
"All the items were long shelflife items. I don't think ordering from Australia would work for fresh food," she said.
Despite the savings, the Kiwi shopper says this was "a crazy little experiment" but she is not sure she would ever order groceries from Australia again.
"The carbon footprint is something I would consider seriously before doing it again."
New Zealand supermarkets have recently been at the centre of a report by the Commerce Commission that recommended the adoption of a mandatory code of conduct to help balance the power big supermarket chains have over suppliers.
Supermarkets across the country are said to be making excess profits of around $1 million a day.
New Zealand's two major players, Foodstuffs (New World, Pak'nSave and Four Square) and Woolworths (Countdown, Super Value and Fresh Choice), have operated effectively as a duopoly, Commerce Commission chair Anna Rawlings said earlier this month.
"We have found that the intensity of competition between the major grocery retailers who dominate the market, Woolworths NZ and Foodstuffs, is muted and competitors wanting to enter or expand face significant challenges.
"While there is an increasingly diverse fringe of other competitors in the sector, they are unable to compete effectively with Woolworths NZ and Foodstuffs on price, product range, and store location to offer the convenience of one-stop shopping for the many different kinds of shopping missions that consumers undertake."
Woolworths and Foodstuffs have a combined market share of about 80 percent in New Zealand.
